TTI LD300 Service Manual page 25

Adjust reference voltage
Note: The internal reference voltage is adjusted to match the gain of the external control input.
Connect: Remove the short circuit and connect a DC supply to the rear panel remote control
voltage input, leaving the negative connection linked to the Load Input negative.
Set: Set the voltage at the remote Control Voltage input to 4·000 V (use the DVM if
necessary).
Select: Enable = in. Slow Start = out; Dropout V = 0V (fully CCW).
Connect: The DVM to DMD (TP3-c) and 0v (TP3-d). Note the reading.
Select: Control = Level B.
Adjust: VR30 for the same DVM reading (at DMD) as above. Switch the Level Control switch
between Level B and External Voltage and check DVM readings agree within ± 0.5mV
Oscillator Frequency
Note: Because of the permitted tolerance on frequency, it should only be necessary to re-adjust
these if a component in the oscillator circuit has been replaced.
Connect: TP1 to frequency counter.
Set: Slew Rate = max. Slew Range = Hi. Level Control = Transient. Enable = in.
Meters = Freq & Duty.
High Frequency range.
Set: Freq Range = Hi.
Adjust Freq control for frequency setting display of about 10kHz.
Adjust: If necessary, adjust VR7 for the counter to match the setting display reading ±20Hz).
Mid Frequency range
Set: Freq Range = Mid. The setting should be about 312Hz.
If necessary, adjust VR8 for the counter to match the setting display reading (±0.5Hz).
Adjust:
Note: It may be helpful to compute the period, and use the counter in period mode.
Low Frequency range
Set: Freq Range = Lo. The setting should be about 10Hz.
Adjust: If necessary, adjust VR9 for the counter to match the setting display reading (±0.02Hz).
Note: This is much easier if the counter is used in period mode.
Duty Cycle
Note: These adjustments change the loading on the Duty Cycle control, so as adjustments are made it
may be necessary to re-set the front panel control to maintain the required Duty Cycle display reading.
If a counter-timer capable of measuring high and low time (from which duty cycle can be calculated) is
not available, then the following procedures using a scope with delayed timebase can be used.
Set Duty Cycle 50%
Connect: If using a scope, connect it to TP1.
Set: Freq Range = Hi, Freq = 10.0 kHz (match the period to the scope X graticule).
Duty Cycle = 50.0%
Scope: Set scope main timebase to 0.1ms/cm. Trigger on +ve edge, DC coupled, at about 50%
point. Enable delayed timebase, set to 2µs/cm, in intensify mode. Adjust the delay to
view the last high to low transition (bright-up at RHS). Switch to B timebase mode.
Adjust: VR20 for identical position of the transition, while switching between positive and
negative trigger polarity.
(Note: Watch the front panel reading and adjust Duty Cycle control as required.)
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